Composition for a polishing pad, polishing pad, and process for preparing the same

ABSTRACT

In the composition according to the embodiment, the content of an unreacted diisocyanate monomer in a urethane-based prepolymer may be controlled to control the physical properties thereof such as gelation time. Thus, since the micropore characteristics, polishing rate, and pad cut rate of a polishing pad obtained by curing the composition according to the embodiment may be controlled, it is possible to efficiently manufacture high-quality semiconductor devices using the polishing pad.

The present application claims priority of Korean patent applicationnumber 10-2018-0169447, Korean patent application number10-2018-0169477, and Korean patent application number 10-2018-0169511filed on Dec. 26, 2018, which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

Embodiments relate to a composition for a porous polyurethane polishingpad for use in a chemical mechanical planarization (CMP) process, aporous polyurethane polishing pad, and a process for preparing the same.

BACKGROUND ART

The chemical mechanical planarization (CMP) process in a process forpreparing semiconductors refers to a step in which a semiconductorsubstrate such as a wafer is fixed to a head and in contact with thesurface of a polishing pad mounted on a platen, and the wafer is thenchemically treated by supplying a slurry while the platen and the headare relatively moved, to thereby mechanically planarize theirregularities on the semiconductor substrate.

A polishing pad is an essential member that plays an important role insuch a CMP process. In general, a polishing pad is composed of apolyurethane resin, which comprises a prepolymer obtained by reacting adiisocyanate monomer and a polyol, a curing agent, a foaming agent, andthe like.

In addition, a polishing pad is provided on its surface with grooves fora large flow of a slurry and pores for supporting a fine flow thereof.The pores may be formed by using a solid phase foaming agent havingvoids, an inert gas, a liquid phase material, a fiber, or the like, orby generating a gas by a chemical reaction (see Korean Laid-open PatentPublication No. 2016-0027075).

DISCLOSURE OF INVENTION Technical Problem

A urethane-based prepolymer used to prepare a polishing pad varies inits physical properties with the monomers, which has a huge impact onthe performance of the chemical mechanical planarization (CMP) process.Thus, it is very important to control the composition and physicalproperties of a urethane-based prepolymer in controlling the performanceof a polishing pad.

As a result of the research conducted by the present inventors, it wasfound that the gelation time is particularly changed by the amount ofunreacted diisocyanate monomers present in a urethane-based prepolymer,which then changes the elongation and pore size of the polishing pad,thereby affecting the CMP performance such as polishing rate.

Accordingly, the embodiments aim to provide a composition whose physicalproperties are controlled by adjusting the amount of unreacteddiisocyanate monomers in a urethane-based prepolymer, a process forpreparing a polishing pad therefrom, a polishing pad prepared from thecomposition, and a process for preparing a semiconductor by using thepolishing pad.

Solution to Problem

According to one embodiment, there is provided a composition, whichcomprises a urethane-based prepolymer, a curing agent, and a foamingagent, wherein the urethane-based prepolymer comprises aprepolymerization reaction product of at least one diisocyanate monomerand at least one polyol, the at least one diisocyanate monomer comprisesat least one aromatic diisocyanate monomer, and the urethane-basedprepolymer comprises an unreacted diisocyanate monomer in an amount of5% by weight to 13% by weight based on the weight of the urethane-basedprepolymer.

According to another embodiment, there is provided a process forpreparing a polishing pad, which comprises preparing a first rawmaterial composition comprising a urethane-based prepolymer, a secondraw material composition comprising a curing agent, and a third rawmaterial composition comprising a foaming agent; preparing a rawmaterial mixture by sequentially or simultaneously mixing the first rawmaterial composition with the second raw material composition and thethird raw material composition; and injecting the raw material mixtureinto a mold and curing it, wherein the urethane-based prepolymercomprises a prepolymerization reaction product of at least onediisocyanate monomer and at least one polyol, the at least onediisocyanate monomer comprises at least one aromatic diisocyanatemonomer, and the urethane-based prepolymer comprises an unreacteddiisocyanate monomer in an amount of 5% by weight to 13% by weight basedon the weight of the urethane-based prepolymer.

According to still another embodiment, there is provided a polishingpad, which comprises a polyurethane resin and a plurality of microporesdispersed in the polyurethane resin, wherein the polyurethane resin isderived from a urethane-based prepolymer, the urethane-based prepolymercomprises a prepolymerization reaction product of at least onediisocyanate monomer and at least one polyol, the at least onediisocyanate monomer comprises at least one aromatic diisocyanatemonomer, and the urethane-based prepolymer comprises an unreacteddiisocyanate monomer in an amount of 5% by weight to 13% by weight basedon the weight of the urethane-based prepolymer.

According to still another embodiment, there is provided a process forpreparing a semiconductor device, which comprises polishing the surfaceof a semiconductor substrate using the polishing pad according to theembodiment.

Advantageous Effects of Invention

In the composition according to the embodiment, the content of anunreacted diisocyanate monomer in a urethane-based prepolymer may becontrolled to control the physical properties thereof such as gelationtime.

Thus, since the micropore characteristics, polishing rate, and pad cutrate of a polishing pad obtained by curing the composition according tothe embodiment may be controlled, it is possible to efficientlymanufacture high-quality semiconductor devices using the polishing pad.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 a to 1 f are scanning electron microscope (SEM) images of poresin the polishing pads of Examples A1, A2, A3, B1, and B2 and ComparativeExample 1.

FIG. 2 a shows the polishing rates of the polishing pads of Examples A1,A2, and A3 and Comparative Example 1.

FIG. 2 b shows the polishing rates of the polishing pads of Examples B1and B2 and Comparative Example 1.

FIG. 3 a shows the pad cut rates of the polishing pads of Examples A1,A2, and A3 and Comparative Example 1.

FIG. 3 b shows the pad cut rates of the polishing pads of Examples B1and B2 and Comparative Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Throughout the description of the embodiments, in the case where anelement is mentioned to be formed on or under another element, it meansnot only that the element is directly formed on or under anotherelement, but also that the element is indirectly formed on or underanother element with other element(s) interposed between them.

In this specification, when a part is referred to as “comprising” anelement, it is to be understood that it may comprise other elements aswell, rather than excluding the other elements, unless specificallystated otherwise.

In addition, all numerical ranges related to the physical properties,dimensions, and the like of a component used herein are to be understoodas being modified by the term “about,” unless otherwise indicated.

In this specification, singular forms are to be interpreted in thecontext of the singular or plural forms, unless the context describesotherwise.

Composition for a Polishing Pad

The composition according to one embodiment comprises a urethane-basedprepolymer, a curing agent, and a foaming agent, wherein theurethane-based prepolymer comprises a prepolymerization reaction productof at least one diisocyanate monomer and at least one polyol, the atleast one diisocyanate monomer comprises at least one aromaticdiisocyanate monomer, and the urethane-based prepolymer comprises anunreacted diisocyanate monomer in an amount of 5% by weight to 13% byweight based on the weight of the urethane-based prepolymer.

According to a specific embodiment, the urethane-based prepolymer in thecomposition comprises an unreacted diisocyanate monomer in an amount of9% by weight to 11% by weight based on the weight of the urethane-basedprepolymer.

According to another specific embodiment, the urethane-based prepolymerin the composition comprises an unreacted NCO group in an amount of 5%by weight to 13% by weight and an unreacted diisocyanate monomer in anamount of 0.1% by weight to 5% by weight, based on the weight of theurethane-based prepolymer.

According to still another specific embodiment, the urethane-basedprepolymer in the composition comprises 10% by weight to 40% by weightof a diisocyanate monomer in which two NCO groups are reacted based onthe total weight of the at least one aromatic diisocyanate monomer.

Urethane-Based Prepolymer

A prepolymer generally refers to a polymer having a relatively lowmolecular weight wherein the degree of polymerization is adjusted to anintermediate level for the sake of conveniently molding a product in theprocess of producing the same. For example, the weight average molecularweight (Mw) of the urethane-based prepolymer may be 500 g/mole to 3,000g/mole, 600 g/mole to 2,000 g/mole, or 700 g/mole to 1,500 g/mole. Aprepolymer may be molded by itself, or after a reaction with anotherpolymerizable compound or a curing agent, to form a final product.

The urethane-based prepolymer is a prepolymerization reaction product ofat least one diisocyanate monomer and at least one polyol.

The at least one diisocyanate monomer may be at least one aromaticdiisocyanate monomer and/or at least one aliphatic diisocyanate monomer.For example, it may be at least one isocyanate selected from the groupconsisting of toluene diisocyanate (TDI), naphthalene-1,5-diisocyanate,p-phenylene diisocyanate, tolidine diisocyanate, diphenylmethanediisocyanate (MDI), hexamethylene diisocyanate (HDI),dicyclohexylmethane diisocyanate (H12MDI), and isophorone diisocyanate.

As a specific example, the at least one diisocyanate monomer maycomprise at least one aromatic diisocyanate monomer, and the at leastone aromatic diisocyanate monomer may comprise toluene 2,4-diisocyanateand toluene 2,6-diisocyanate.

As another specific example, the at least one diisocyanate monomer maycomprise at least one aliphatic diisocyanate monomer, and the at leastone aliphatic diisocyanate monomer may be diphenylmethane diisocyanate(MDI), hexamethylene diisocyanate (HDI), dicyclohexylmethanediisocyanate (H12MDI), or the like.

Chain Configuration in the Prepolymer

The urethane-based prepolymer comprises polymerization reactants ofvarious molecular weights between a diisocyanate monomer and a polyol.

For example, in the urethane-based prepolymer, the diisocyanate monomermay form a chain in the prepolymer by reaction of at least one NCO group(i.e., reaction of two NCO groups or one NCO group).

The reaction of the NCO group in the diisocyanate monomer includes areaction with a polyol or a side reaction with another compound, and itis not specifically limited. For example, the reaction of the NCO groupmay include a chain extension reaction or a crosslinking reaction.

As an example, the reaction of the NCO group comprises a urethanereaction in which the NCO group and the OH group are reacted to form aurethane group (—NH—C(═O)—O—) in the course of reacting a diisocyanatemonomer and a polyol to prepare the urethane-based prepolymer. As arepresentative example, the NCO group of toluene diisocyanate (TDI) andthe OH group of diethylene glycol (DEG) may be subjected to a urethanereaction to form a chain as shown in the following formula.

As another example, the reaction of the NCO group may include a ureareaction with an amine compound and, as a result, form a urea group(—NH—C(═O)—NH—).

As another example, the reaction of the NCO group may further include acrosslinking reaction. For example, it may further include acrosslinking reaction to form an allophanate group or a biuret group.

The at least one diisocyanate monomer used in the preparation of theurethane-based prepolymer may comprise at least one aromaticdiisocyanate monomer. Such at least one aromatic diisocyanate monomermay participate in the prepolymerization reaction at a high rate.

For example, the urethane-based prepolymer may comprise an aromaticdiisocyanate monomer in which at least one NCO group is reacted in anamount of 50% by weight to 99% by weight, 60% by weight to 99% byweight, 70% by weight to 99% by weight, 80% by weight to 99% by weight,or 90% by weight to 99% by weight, based on the total weight of the atleast one aromatic diisocyanate monomer.

In particular, the urethane-based prepolymer may comprise an aromaticdiisocyanate monomer in which two NCO groups are reacted in an amount of10% by weight to 40% by weight, 10% by weight to 35% by weight, 15% byweight to 35% by weight, 20% by weight to 35% by weight, 25% by weightto 35% by weight, 10% by weight to 30% by weight, 20% by weight to 30%by weight, or 10% by weight to 25% by weight, based on the total weightof the at least one aromatic diisocyanate monomer.

As a specific example, the urethane-based prepolymer may comprise thearomatic diisocyanate monomer in which two NCO groups are reacted in anamount of 15% by weight to 25% by weight based on the total weight ofthe at least one aromatic diisocyanate monomer.

In addition, the urethane-based prepolymer may comprise an aromaticdiisocyanate monomer in which one NCO group is reacted in an amount of50% by weight to 90% by weight, 60% by weight to 90% by weight, 70% byweight to 90% by weight, 80% by weight to 90% by weight, 50% by weightto 80% by weight, or 60% by weight to 80% by weight, based on the totalweight of the at least one aromatic diisocyanate monomer.

As a specific example, the urethane-based prepolymer may comprise thearomatic diisocyanate monomer in which one NCO group is reacted in anamount of 50% by weight to 80% by weight based on the total weight ofthe at least one aromatic diisocyanate monomer.

In such event, the urethane-based prepolymer may comprise the aromaticdiisocyanate monomer in which two NCO groups are reacted and thearomatic diisocyanate monomer in which one NCO group is reacted at aweight ratio of 0.1:1 to 1:1, 0.2:1 to 1:1, 0.2:1 to 0.5:1, 0.3:1 to1:1, or 0.3:1 to 0.5:1.

As a specific example, the urethane-based prepolymer may comprise thearomatic diisocyanate monomer in which two NCO groups are reacted andthe aromatic diisocyanate monomer in which one NCO group is reacted at aweight ratio of 0.2:1 to 0.5:1.

More specifically, the at least one aromatic diisocyanate monomer maycomprise toluene 2,4-diisocyanate and toluene 2,6-diisocyanate. In suchevent, the urethane-based prepolymer may comprise toluene2,4-diisocyanate in which at least one NCO group is reacted and toluene2,6-diisocyanate in which at least one NCO group is reacted in an amountof 80% by weight to 98% by weight, 85% by weight to 98% by weight, 90%by weight to 98% by weight, 93% by weight to 98% by weight, or 95% byweight to 98% by weight, based on the total weight of the at least onearomatic diisocyanate monomer.

In addition, the urethane-based prepolymer may comprise toluene2,4-diisocyanate in which two NCO groups are reacted in an amount of 10%by weight to 40% by weight, 10% by weight to 35% by weight, 15% byweight to 35% by weight, 20% by weight to 35% by weight, 10% by weightto 30% by weight, 20% by weight to 30% by weight, or 10% by weight to25% by weight, based on the total weight of the at least one aromaticdiisocyanate monomer.

As a specific example, the urethane-based prepolymer may comprisetoluene 2,4-diisocyanate in which two NCO groups are reacted in anamount of 10% by weight to 30% by weight based on the total weight ofthe at least one aromatic diisocyanate monomer.

In addition, the urethane-based prepolymer may comprise toluene2,4-diisocyanate in which one NCO group is reacted in an amount of 40%by weight to 80% by weight, 45% by weight to 75% by weight, 45% byweight to 70% by weight, 45% by weight to 65% by weight, 45% by weightto 60% by weight, 60% by weight to 75% by weight, or 60% by weight to70% by weight, based on the total weight of the at least one aromaticdiisocyanate monomer.

As a specific example, the urethane-based prepolymer may comprisetoluene 2,4-diisocyanate in which one NCO group is reacted in an amountof 50% by weight to 65% by weight based on the total weight of the atleast one aromatic diisocyanate monomer.

In addition, the urethane-based prepolymer may comprise toluene2,6-diisocyanate in which one NCO group is reacted in an amount of 1% byweight to 30% by weight, 5% by weight to 25% by weight, 10% by weight to25% by weight, 10% by weight to 20% by weight, 5% by weight to 20% byweight, 5% by weight to 15% by weight, or 10% by weight to 15% byweight, based on the total weight of the at least one aromaticdiisocyanate monomer.

As a specific example, the urethane-based prepolymer may comprisetoluene 2,6-diisocyanate in which one NCO group is reacted in an amountof 10% by weight to 20% by weight based on the total weight of the atleast one aromatic diisocyanate monomer.

Unreacted Diisocyanate Monomer

In addition, some of the compounds used in the reaction for preparingthe urethane-based prepolymer may not participate in the reaction.

Thus, a compound that has not participated in the reaction may bepresent in the urethane-based prepolymer.

Specifically, the urethane-based prepolymer may comprise an unreacteddiisocyanate monomer. In this specification, the “unreacted diisocyanatemonomer” refers to a diisocyanate monomer in which both of the two NCOgroups remain unreacted.

The urethane-based prepolymer may comprise an unreacted diisocyanatemonomer in an amount of 7% by weight to 10% by weight, 7% by weight to9%, by weight, 7% by weight to 8% by weight, 8% by weight to 10% byweight, 8.5% by weight to 10% by weight, 9% by weight to 10% by weight,or 8% by weight to 9% by weight, based on the weight of theurethane-based prepolymer.

The unreacted diisocyanate monomer present in the urethane-basedprepolymer may comprise an unreacted aromatic diisocyanate monomer.

For example, the urethane-based prepolymer may comprise an unreactedaromatic diisocyanate monomer in an amount of 0.1% by weight to 5% byweight, 0.1% by weight to 3% by weight, 0.1% by weight to 2.3% byweight, 0.1% by weight to 1.5% by weight, 0.1% by weight to 1% byweight, 0.5% by weight to 2% by weight, 1% by weight to 2% by weight, 1%by weight to 3% by weight, or 1% by weight to 5% by weight, based on theweight of the urethane-based prepolymer.

As a specific example, the urethane-based prepolymer may comprise anunreacted aromatic diisocyanate monomer in an amount of 2% by weight to4% by weight based on the weight of the urethane-based prepolymer.

When the at least one aromatic diisocyanate monomer used in the reactionfor preparing the urethane-based prepolymer comprises toluene2,4-diisocyanate and toluene 2,6-diisocyanate, toluene 2,6-diisocyanateamong them is relatively low in reactivity and thus may be present inthe urethane-based prepolymer without reacting with a polyol. Forexample, the urethane-based prepolymer may comprise unreacted toluene2,6-diisocyanate in an amount of 0.1% by weight to 10% by weight, 0.1%by weight to 8% by weight, 0.1% by weight to 6% by weight, 0.1% byweight to 4% by weight, 0.5% by weight to 4% by weight, or 1% by weightto 4% by weight, based on the weight of the urethane-based prepolymer.

As a specific example, the urethane-based prepolymer may compriseunreacted toluene 2,6-diisocyanate in an amount of 0.1% by weight to 3%by weight based on the weight of the urethane-based prepolymer.

In addition, the unreacted diisocyanate monomer present in theurethane-based prepolymer may comprise an unreacted aliphaticdiisocyanate monomer.

For example, the urethane-based prepolymer may comprise an unreactedaliphatic diisocyanate monomer in an amount of 1% by weight to 20% byweight, 1% by weight to 15% by weight, 1% by weight to 10% by weight, 5%by weight to 20% by weight, 10% by weight to 20% by weight, or 5% byweight to 15% by weight, based on the weight of the urethane-basedprepolymer.

In addition, the urethane-based prepolymer may comprise the unreactedaromatic diisocyanate monomer and the unreacted aliphatic diisocyanatemonomer at a weight ratio of 0.01:1 to 1:1, 0.05:1 to 0.8:1, 0.05:1 to0.5:1, or 0.05:1 to 0.3:1.

As a specific example, the urethane-based prepolymer may comprise theunreacted aromatic diisocyanate monomer and the unreacted aliphaticdiisocyanate monomer at a weight ratio of 0.05:1 to 0.7:1.

Content of Unreacted NCO Group

The urethane-based prepolymer may have an unreacted NCO group at theterminal of a polymer, oligomer, or monomer contained therein.

As a specific example, the urethane-based prepolymer may comprise anunreacted NCO group in an amount of 5% by weight to 15% by weight, 5% byweight to 13% by weight, 5% by weight to 10% by weight, 7% by weight to13% by weight, 7% by weight to 10% by weight, 7.5% by weight to 10% byweight, 9% by weight to 11% by weight, or 9% by weight to 10% by weight,based on the weight of the urethane-based prepolymer.

As a specific example, the urethane-based prepolymer may comprise theunreacted NCO group in an amount of 7% by weight to 10% by weight basedon the weight of the urethane-based prepolymer. In such event, theurethane-based prepolymer may comprise the unreacted aromaticdiisocyanate monomer in an amount of 1% by weight to 3% by weight basedon the weight of the urethane-based prepolymer. In addition, in suchevent, the composition may have a gelation time of 100 seconds to 115seconds.

Polyol

The polyol used in the above embodiments is a conventional polyol widelyrecognized in the field of polyurethane preparation. It may have one,two, or more hydroxyl groups and is not particularly limited in terms ofthe kind and molecular weight.

In general, a polyol is distinguished from a monomolecular alcohol. Itmay refer to a compound that comprises at least one hydroxyl group andhas a certain molecular weight, for example, a weight average molecularweight of 200 or more, specifically 300 to 3,000.

Specific examples of the polyol include polyether polyols, polyesterpolyols, polycarbonate polyols, polycaprolactone polyols, and the like.

Specifically, a polyether polyol is a compound that contains two or morealkylene ether (or alkylene glycol) repeat units. It may have amolecular weight that reaches not only a low molecule but also anoligomer to a polymer depending on the number of repeats of the alkyleneether units.

In addition, a polyol may refer to a composition of a mixture of thesecompounds of various molecular weights. It may comprise such an alcoholas ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG),propanediol (PDO), methyl propanediol (MP-diol), and the like.

Curing Agent

The curing agent may be at least one of an amine compound and an alcoholcompound. Specifically, the curing agent may comprise at least onecompound selected from the group consisting of an aromatic amine, analiphatic amine, an aromatic alcohol, and an aliphatic alcohol.

For example, the curing agent may be at least one selected from thegroup consisting of 4,4′-methylenebis(2-chloroaniline) (MOCA),diethyltoluenediamine (DETDA), diaminodiphenyl methane, diaminodiphenylsulphone, m-xylylene diamine, isophoronediamine, ethylenediamine,diethylenetriamine, triethylenetetramine, polypropylenediamine,polypropylenetriamine, ethylene glycol, diethylene glycol, dipropyleneglycol, butanediol, hexanediol, glycerin, trimethylolpropane, andbis(4-amino-3-chlorophenyl)methane.

The urethane-based prepolymer and the curing agent may be mixed at amolar equivalent ratio of 1:0.8 to 1:1.2, or a molar equivalent ratio of1:0.9 to 1:1.1, based on the number of moles of the reactive groups ineach molecule. Here, “the number of moles of the reactive groups in eachmolecule” refers to, for example, the number of moles of the isocyanategroup in the urethane-based prepolymer and the number of moles of thereactive groups (e.g., amine group, alcohol group, and the like) in thecuring agent. Therefore, the urethane-based prepolymer and the curingagent may be fed at a constant rate during the mixing process bycontrolling the feeding rate such that the urethane-based prepolymer andthe curing agent are fed in amounts per unit time that satisfies themolar equivalent ratio exemplified above.

Foaming Agent

The foaming agent is not particularly limited as long as it is commonlyused for forming voids in a polishing pad.

For example, the foaming agent may be at least one selected from a solidphase foaming agent having a void structure, a liquid phase foamingagent using a volatile liquid, and an inert gas.

The solid phase foaming agent may be microcapsules (hereinafter,referred to as “thermally expanded microcapsules”), whose size has beenadjusted by a thermal expansion. The thermally expanded microcapsulesmay be obtained by thermally expanding thermally expandablemicrocapsules. Since the thermally expanded microcapsules in a structureof already expanded micro-balloons have a uniform particle diameter,they have the advantage that the diameter of pores can be uniformlycontrolled. Specifically, the solid phase foaming agent may be in astructure of micro-balloons having an average particle diameter of 5 μmto 200 μm.

The thermally expandable microcapsule may comprise a shell comprising athermoplastic resin; and a foaming agent encapsulated inside the shell.The thermoplastic resin may be at least one selected from the groupconsisting of a vinylidene chloride-based copolymer, anacrylonitrile-based copolymer, a methacrylonitrile-based copolymer, andan acrylic-based copolymer. Furthermore, the foaming agent may be atleast one selected from the group consisting of hydrocarbons having 1 to7 carbon atoms.

The solid phase foaming agent may be employed in an amount of 0.1 partby weight to 2 parts by weight based on 100 parts by weight of theurethane-based prepolymer. Specifically, the solid phase foaming agentmay be employed in an amount of 0.3 parts by weight to 1.5 parts byweight or 0.5 parts by weight to 1.0 parts by weight, based on 100 partsby weight of the urethane-based prepolymer.

The kind of the inert gas is not particularly limited as long as it is agas that does not participate in the reaction between the urethane-basedprepolymer and the curing agent. For example, the inert gas may be atleast one selected from the group consisting of nitrogen gas (N₂),carbon dioxide (CO₂), argon gas (Ar), and helium (He). Specifically, theinert gas may be nitrogen gas (N₂) or carbon dioxide (CO₂).

The inert gas may be fed in a volume of 10% to 30% based on the totalvolume of the polyurethane composition. Specifically, the inert gas maybe fed in a volume of 15% to 30% based on the total volume of thepolyurethane composition.

Gelation Time

The composition takes a certain time to gelate by curing, which isreferred to as gelation time.

The gelation time of the composition may be at least 50 seconds, atleast 70 seconds, at least 80 seconds, or at least 100 seconds. Forexample, the gelation time of the composition may be 50 seconds to 200seconds, 50 seconds to 150 seconds, 50 seconds to 100 seconds, 100seconds to 200 seconds, or 150 seconds to 200 seconds. As a specificexample, the composition may have a gelation time of 80 seconds to 130seconds.

The gelation time may be, for example, a value measured at 70° C.

Characteristics Upon Gelation

The mechanical properties of the composition such as tensile strength,elongation, hardness, and the like may be adjusted to specific rangesupon curing.

For example, the tensile strength of the composition upon curing may be5 N/mm² to 30 N/mm², 10 N/mm² to 25 N/mm², 10 N/mm² to 20 N/mm², or 15N/mm² to 30 N/mm².

In addition, the elongation of the composition upon curing may be 50% to300%, 100% to 300%, 150% to 250%, or 100% to 200%.

In addition, the hardness of the composition upon curing may be 30 ShoreD to 80 Shore D, 40 Shore D to 70 Shore D, 50 Shore D to 70 Shore D, 40Shore D to 60 Shore D, or 50 Shore D to 60 Shore D.

As a specific example, the composition upon curing may have a tensilestrength of 10 N/mm² to 23 N/mm², an elongation of 80% to 250%, and ahardness of 40 Shore D to 65 Shore D.

The composition may have a plurality of micropores upon curing.

The average size of the micropores may be 10 μm to 50 μm, 20 μm to 50μm, 20 μm to 40 μm, 20 μm to 30 μm, or 30 μm to 50 μm.

In addition, the polishing rate (or removal rate) of the compositionupon curing may be 3,000 Å/50 seconds to 5,000 Å/50 seconds, 3,000 Å/50seconds to 4,000 Å/50 seconds, 4,000 Å/50 seconds to 5,000 Å/50 seconds,or 3,500 Å/50 seconds to 4,500 Å/50 seconds.

In addition, the pad cut rate of the composition upon curing may be 30μm/hr to 60 μm/hr, 30 μm/hr to 50 μm/hr, 40 μm/hr to 60 μm/hr, or 40μm/hr to 50 μm/hr.

Process for Preparing a Polishing Pad

The process for preparing a polishing pad according to one embodimentcomprises molding the composition according to the embodiment whilecuring it.

That is, the process for preparing a polishing pad according to oneembodiment comprises preparing a first raw material compositioncomprising a urethane-based prepolymer, a second raw materialcomposition comprising a curing agent, and a third raw materialcomposition comprising a foaming agent; preparing a raw material mixtureby sequentially or simultaneously mixing the first raw materialcomposition with the second raw material composition and the third rawmaterial composition; and injecting the raw material mixture into a moldand curing it, wherein the urethane-based prepolymer comprises aprepolymerization reaction product of at least one diisocyanate monomerand at least one polyol, the at least one diisocyanate monomer comprisesat least one aromatic diisocyanate monomer, and the urethane-basedprepolymer comprises 5% by weight to 13% by weight of the unreacteddiisocyanate monomer based on the weight of the urethane-basedprepolymer.

Specifically, the step of preparing the raw material mixture may becarried out by mixing the first raw material composition with the secondraw material composition, followed by further mixing thereof with thethird raw material composition, or by mixing the first raw materialcomposition with the third raw material composition, followed by furthermixing thereof with the second raw material composition.

In addition, the step of preparing the raw material mixture may becarried out under the condition of 50° C. to 150° C. If necessary, itmay be carried out under vacuum defoaming conditions.

The step of injecting the raw material mixture into a mold and curing itmay be carried out under the temperature condition of 60° C. to 120° C.and the pressure condition of 50 kg/m² to 200 kg/m².

In addition, the above preparation process may further comprise thesteps of cutting the surface of a polishing pad thus obtained, machininggrooves on the surface thereof, bonding with the lower part, inspection,packaging, and the like. These steps may be carried out in aconventional manner for preparing a polishing pad.

Polishing Pad

The polishing pad according to one embodiment comprises a cured productof the composition according to the embodiment and a plurality ofmicropores dispersed in the cured product.

That is, the polishing pad according to one embodiment comprises apolyurethane resin and a plurality of micropores dispersed in thepolyurethane resin, wherein the polyurethane resin is derived from aurethane-based prepolymer, the urethane-based prepolymer comprises aprepolymerization reaction product of at least one diisocyanate monomerand at least one polyol, the at least one diisocyanate monomer comprisesat least one aromatic diisocyanate monomer, and the urethane-basedprepolymer comprises 5% by weight to 13% by weight of the unreacteddiisocyanate monomer based on the weight of the urethane-basedprepolymer.

The polishing pad is comprised of a polyurethane resin, and thepolyurethane resin may comprise a cured product (i.e., polymer) of aurethane-based prepolymer having an isocyanate terminal group. Theweight average molecular weight (Mw) of the polyurethane resin may be500 g/mole to 1,000,000 g/mole, 5,000 g/mole to 1,000,000 g/mole, 50,000g/mole to 1,000,000 g/mole, 100,000 g/mole to 700,000 g/mole, or 500g/mole to 3,000 g/mole.

The thickness of the polishing layer may be 0.8 mm to 5.0 mm, 1.0 mm to4.0 mm, 1.0 mm to 3.0 mm, 1.5 mm to 2.5 mm, 1.7 mm to 2.3 mm, or 2.0 mmto 2.1 mm. Within the above range, the basic physical properties as apolishing pad can be sufficiently exhibited while the particle sizevariation between the upper and lower portions is minimized.

The specific gravity of the polishing pad may be 0.6 g/cm³ to 0.9 g/cm³or 0.7 g/cm³ to 0.85 g/cm³.

In addition, the polishing pad may have the same physical properties andpore characteristics as those of the composition according to the aboveembodiment upon curing in addition to the physical propertiesexemplified above.

The hardness of the polishing pad may be 30 Shore D to 80 Shore D, 40Shore D to 70 Shore D, 50 Shore D to 70 Shore D, 40 Shore D to 60 ShoreD, or 50 Shore D to 60 Shore D.

The tensile strength of the polishing pad may be 5 N/mm² to 30 N/mm², 10N/mm² to 25 N/mm², 10 N/mm² to 20 N/mm², or 15 N/mm² to 30 N/mm².

The elongation of the polishing pad may be 50% to 300%, 100% to 300%,150% to 250%, or 100% to 200%.

The micropores are present as dispersed in the polyurethane resin.

The average size of the micropores may be 10 μm to 50 μm, 20 μm to 50μm, 20 μm to 40 μm, 20 μm to 30 μm, or 30 μm to 50 μm. As a specificexample, the micropores may have an average size of 20 μm to 25 μm.

In addition, 100 to 300, 150 to 300, or 100 to 250 of the micropores maybe contained per an area of 0.3 cm² of the polishing pad.

In addition, the total area of the micropores may be 30% to 60%, 35% to50%, or 35% to 43% based on the total area of the polishing pad.

In addition, the micropores may be contained in an amount of 30 to 70%by volume, or 40 to 60% by volume, based on the total volume of thepolishing pad.

The polishing rate (or removal rate) of the polishing pad may be 3,000Å/50 seconds to 5,000 Å/50 seconds, 3,000 Å/50 seconds to 4,000 Å/50seconds, 4,000 Å/50 seconds to 5,000 Å/50 seconds, or 3,500 Å/50 secondsto 4,500 Å/50 seconds. The polishing rate may be an initial polishingrate immediately after curing of the polishing pad (i.e., immediatelyafter the preparation thereof). If the initial polishing rate is withinthe above preferred range, it is advantageous to suppressing the padglazing phenomenon, thereby maintaining an appropriate level ofexcellent polishing rate in subsequent polishing processes repeatedlycarried out.

As a specific example, the micropores may have an average size of 20 μmto 25 μm, and the polishing pad may have a polishing rate (or removalrate) of 3,500 Å/50 seconds to 5,000 Å/50 seconds

In addition, the pad cut rate of the polishing pad may be 30 μm/hr to 60μm/hr, 30 μm/hr to 50 μm/hr, 40 μm/hr to 60 μm/hr, or 40 μm/hr to 50μm/hr.

The polishing pad may have grooves on its surface for mechanicalpolishing. The grooves may have a depth, a width, and a spacing asdesired for mechanical polishing, which are not particularly limited.

The polishing pad according to another embodiment may comprise an upperpad and a lower pad, wherein the upper pad may have the same compositionand physical properties as those of the polishing pad according to theembodiment.

The lower pad serves to support the upper pad and to absorb and dispersean impact applied to the upper pad. The lower pad may comprise anonwoven fabric or a suede.

In addition, an adhesive layer may be interposed between the upper padand the lower pad.

The adhesive layer may comprise a hot melt adhesive. The hot meltadhesive may be at least one selected from the group consisting of apolyurethane resin, a polyester resin, an ethylene-vinyl acetate resin,a polyamide resin, and a polyolefin resin. Specifically, the hot meltadhesive may be at least one selected from the group consisting of apolyurethane resin and a polyester resin.

Process for Preparing a Semiconductor Device

The process for preparing a semiconductor device according to oneembodiment comprises polishing the surface of a semiconductor substrateusing the polishing pad according to the embodiment.

That is, process for preparing a semiconductor device according to oneembodiment comprises polishing the surface of a semiconductor substrateusing a polishing pad, wherein the polishing pad comprises apolyurethane resin and a plurality of micropores dispersed in thepolyurethane resin, wherein the polyurethane resin is derived from aurethane-based prepolymer, the urethane-based prepolymer comprises aprepolymerization reaction product of at least one diisocyanate monomerand at least one polyol, the at least one diisocyanate monomer comprisesat least one aromatic diisocyanate monomer, and the urethane-basedprepolymer comprises 5% by weight to 13% by weight of the unreacteddiisocyanate monomer based on the weight of the urethane-basedprepolymer.

Specifically, once the polishing pad according to the embodiment isattached to a platen, a semiconductor substrate is disposed on thepolishing pad. In such event, the surface of the semiconductor substrateis in direct contact with the polishing surface of the polishing pad. Apolishing slurry may be sprayed on the polishing pad for polishing.Thereafter, the semiconductor substrate and the polishing pad rotaterelatively to each other, so that the surface of the semiconductorsubstrate is polished.

The polishing pad according to the embodiment has excellent elongation,hardness, micropore characteristics, polishing rate, and the like sinceit is obtained by curing a urethane-based prepolymer having a controlledcomposition. Thus, it is possible to effectively manufacture asemiconductor device of high quality by using the polishing pad.

MODE FOR THE INVENTION

Hereinafter, the present invention is explained in detail by thefollowing Examples. However, the scope of the present invention is notlimited thereto.

Examples and Comparative Example

A 4-necked flask was charged with toluene 2,4-diisocyanate (2,4-TDI),toluene 2,6-diisocyanate (2,6-TDI), polytetramethylene ether glycol(PTMEG), and dicyclohexylmethane diisocyanate (H12MDI), which werereacted at 80° C., followed by further addition of diethylene glycol(DEG) and further reaction for 2 hours at 80° C. to prepare aurethane-based prepolymer.

A casting machine equipped with tanks and feeding lines for aprepolymer, a curing agent, an inert gas, and a foaming agent wasprovided. The urethane-based prepolymer prepared above, a curing agent(bis(4-amino-3-chlorophenyl)methane, Ishihara), an inert gas (N₂), aliquid phase foaming agent (FC3283, 3M), a solid phase foaming agent(Akzonobel), and a silicone-based surfactant (Evonik) were charged toeach tank. The raw materials were stirred while they were fed to themixing head at constant rates through the respective feeding lines. Insuch event, the prepolymer and the curing agent were fed at anequivalent ratio of 1:1 and at a total rate of 10 kg/min.

The mixed raw materials were injected into a mold (1,000 mm×1,000 mm×3mm) and reacted to obtain a molded article in the form of a solid cake.Thereafter, the top and bottom of the molded article were each cut by athickness of 0.5 mm to obtain a top pad having a thickness to 2 mm.

Thereafter, the upper pad was subjected to surface milling and grooveforming steps and laminated with a lower pad by a hot melt adhesive.

Specific process conditions for preparing the upper pad are summarizedin the table below.

TABLE 1 Exam- Exam- Exam- Item ple A1 ple A2 ple A3 C. Ex. 1 UpperContent of 9.2% by 9.2% by 9.2% by 15% by pad unreacted weight weightweight weight NCO group in prepolymer Casting mold Single Single SingleSingle layer layer layer layer Sheet ma- sequen- sequen- sequen- sequen-chining (cast- tial tial tial tial ing, cutting, and grooving)Prepolymer 100 100 100 100 (part by weight) Surfactant 0.2 to 1.5 0.2 to1.5 0.2 to 1.5 0.2 to 1.5 (part by weight) Solid phase 0.5 to 1.0 0.5 to1.0 0.5 to 1.0 0.5 to 1.0 foaming agent (part by weight) Inert gas 0.5to 1.5 0.5 to 1.5 0.5 to 1.5 0.5 to 1.5 feeding rate (liter/min)

TABLE 2 Exam- Exam- Item ple B1 ple B2 C. Ex. 1 Upper Content ofunreacted 9.2% by 8.0% by 15% by pad NCO group in weight weight weightprepolymer Casting mold Single Single Single layer layer layer Sheetmachining sequential sequential sequential (casting, cutting, andgrooving) Prepolymer (part 100 100 100 by weight) Surfactant (part 0.2to 1.5 0.2 to 1.5 0.2 to 1.5 by weight) Solid phase 0.5 to 1.0 0.5 to1.0 0.5 to 1.0 foaming agent (part by weight) Inert gas 0.5 to 1.5 0.5to 1.5 0.5 to 1.5 feeding rate (liter/min)

Test Example

The urethane-based prepolymers or the polishing pads obtained in theExamples and Comparative Example were tested for the following items.

(1) Composition of the Prepolymer

5 mg of a prepolymer sample was dissolved in CDCl₃ and subjected to¹H-NMR and ¹³C-NMR analyses using a nuclear magnetic resonance (NMR)device (JEOL 500 MHz, 90° pulse) at room temperature. The peaks ofreacted or unreacted methyl groups of TDI in the NMR data thus obtainedwere integrated, whereby the content of a reacted or unreacted aromaticdiisocyanate monomer in the prepolymer was calculated.

Specifically, when the weight of 2,4-TDI (hereinafter referred to as“4-reacted 2,4-TDI”) in which only the NCO group located at the4-position among the two NCO groups had been reacted with a polyol is100 parts by weight, the respective weights of 2,4-TDI (hereinafterreferred to as “2,4-reacted 2,4-TDI”) in which both NCO groups had beenreacted with a polyol to form a chain, 2,6-TDI (hereinafter referred toas “unreacted 2,6-TDI”) in which no NCO group had been reacted with apolyol, and 2,6-TDI (hereinafter referred to as “2-reacted 2,6-TDI”) inwhich only NCO group located at the 2-position or the 6-position of thetwo NCO groups had been reacted with a polyol were calculated. (Inaddition, 2,4-TDI in which the NCO group located at the 2-position hadbeen reacted and 2,6-TDI in which both NCO groups had been reacted werehardly detected.)

The results are shown in the table below.

TABLE 3 Exam- Exam- Exam- Item ple A1 ple A2 ple A3 C. Ex. 1 Content4-reacted 100.00 100.00 100.00 100.00 (parts 2,4-TDI by weight)2,4-reacted 30.22 32.00 32.47 13.90 2,4-TDI unreacted 10.94 8.75 6.3321.22 2,6-TDI 2-reacted 11.30 19.88 21.96 9.59 2,6-TDI Total content152.46 160.63 160.76 144.71 of TDI

TABLE 4 Item Example B1 Example B2 C. Ex. 1 Content 4-reacted 2,4-TDI100.00 100.00 100.00 (parts 2,4-reacted 2,4-TDI 36.63 49.65 13.90 byweight) unreacted 2,6-TDI 7.83 3.65 21.22 2-reacted 2,6-TDI 21.67 26.179.59 Total content of TDI 166.13 179.47 144.71

TABLE 5 Exam- Exam- Exam- Item ple A1 ple A2 ple A3 C. Ex. 1 ContentUnreacted TDI 7.18 5.45 3.94 14.66 (% by TDI with two 19.82 19.92 20.209.61 weight) reacted NCO (Total TDI groups (c1) weight) TDI with one73.00 74.63 75.86 75.73 reacted NCO group (c2) TDI with at 92.82 94.5596.06 85.34 least one reacted NCO group c1/c2 weight ratio 0.27 0.270.27 0.13

TABLE 6 Item Example B1 Example B2 C. Ex. 1 Content Unreacted TDI 4.712.03 14.66 (% by weight) TDI with two 22.05 27.66 9.61 (Total TDIreacted NCO weight) groups (c1) TDI with one 73.24 70.30 75.73 reactedNCO group (c2) TDI with at 95.29 97.97 85.34 least one reacted NCO groupc1/c2 weight ratio 0.30 0.39 0.13

TABLE 7 Exam- Exam- Exam- Item ple A1 ple A2 ple A3 C. Ex. 1 ContentUnreacted 2.39 1.81 1.31 6.28 (% by TDI (c3) weight) (Urethane-Unreacted 7.62 7.62 7.62 7.60 based H12MDI prepolymer (c4) weight) c3 +c4 10.01 9.43 8.93 13.88 c3/c4 weight ratio 0.31 0.24 0.17 0.83

TABLE 8 Exam- Exam- Item ple B1 ple B2 C. Ex. 1 Content Unreacted 1.460.68 6.28 (% by weight) TDI (c3) (Urethane-based Unreacted 7.60 7.607.60 prepolymer weight) H12MDI (c4) c3 + c4 9.06 8.28 13.88 c3/c4 weightratio 0.19 0.09 0.83

(2) Hardness

Each sample was cut to 5 cm×5 cm (thickness: 2 mm) and stored at atemperature of 25° C. for 12 hours to measure the Shore D hardness andAsker C hardness using a hardness tester.

(3) Specific Gravity

Each sample was cut to 5 cm×5 cm (thickness: 2 mm) and stored at atemperature of 25° C. for 12 hours to measure the specific gravity usinga gravimeter.

(4) Tensile Strength

Each sample was cut to 4 cm×1 cm (thickness: 2 mm). The ultimatestrength immediately before the fracture was measured while thepolishing pad was tested at a rate of 50 mm/min using a universaltesting machine (UTM).

(5) Elongation

Each sample was cut to 4 cm×1 cm (thickness: 2 mm). The maximumdeformation immediately before the fracture was measured, and the ratioof the maximum deformation to the initial length was expressed inpercent (%).

(5) Gelation Time

The prepolymer and the curing agent were mixed at an equivalent ratio of1:1, and the time taken until the mixture stirred at 5,000 rpm wasgelated at 70° C.

The results are shown in the table below.

Exam- Exam- Exam- Item Evaluation ple A1 ple A2 ple A3 C. Ex. 1 UpperThickness 2 2 2 2 pad (mm) Hardness 63 61 58 68 (Shore D) Specific 0.80.8 0.8 0.8 gravity (g/cc) Tensile 21 18 15 25 strength (N/mm²)Elongation 125 200 230 63 (%) Gelation 108 115 121 50 time (s) LowerType Nonwoven Nonwoven Nonwoven Nonwoven pad fabric fabric fabric fabricthickness 1.1 1.1 1.1 1.1 (mm) Hardness 70 70 70 70 (Asker C) Laminatedthickness 3.32 3.32 3.32 3.32 pad (mm) Compression 1.05 1.05 1.05 1.05rate (%)

TABLE 10 Exam- Exam- Item Evaluation ple B1 ple B2 C. Ex. 1 Upper padThickness (mm) 2 2 2 Hardness (Shore D) 60 52 68 Specific gravity (g/cc)0.8 0.8 0.8 Tensile strength (N/mm²) 21 18 25 Elongation (%) 125 200 63Gelation time (s) 108 121 50 Lower pad Type Nonwoven Nonwoven Nonwovenfabric fabric fabric thickness (mm) 1.1 1.1 1.1 Hardness (Asker C) 70 7070 Laminated thickness (mm) 3.32 3.32 3.32 pad Compression rate (%) 1.051.05 1.05

(7) Pore Characteristics

The pores of each polishing pad were observed by scanning electronmicroscopy (SEM) and are shown in FIGS. 1 a to 1 f . As shown in FIGS. 1a to 1 f , the pores of the polishing pad of the Examples are finely anduniformly distributed over a large area.

In addition, the pore characteristics of the pores were calculated basedon the SEM images and summarized in the table below.

-   -   Number average diameter: average of the sum of the pore        diameters divided by the number of pores on the SEM image    -   Number of pores: Number of pores per 0.3 cm² on the SEM image    -   Pore area ratio: percentage of the area of the pores relative to        the total area of the SEM image

TABLE 11 Item Example A1 Example A2 Example A3 C. Ex. 1 Number average22.454 22.591 23.313 20.523 diameter (μm) Number of pores 176 200 167162 (per 0.3 cm²) Pore area ratio (%) 38.165 44.067 38.896 38.245

TABLE 12 Item Example B1 Example B2 C. Ex. 1 Number average 22.45423.313 20.523 diameter (μm) Number of pores 176 167 162 (per 0.3 cm²)Pore area ratio (%) 38.165 38.896 38.245

(8) Polishing Rate (Removal Rate)

The initial polishing rate immediately after the polishing pad had beenprepared was measured as follows.

A silicon-based semiconductor substrate having a diameter of 300 mm wasdeposited with silicon oxide by a CVD process. The polishing pad wasmounted on a CMP machine, and the semiconductor substrate was set withthe silicon oxide layer thereof facing the polishing surface of thepolishing pad. The silicon oxide layer was polished under a polishingload of 4.0 psi while it was rotated at a speed of 150 rpm for 60seconds and a calcined silica slurry was supplied onto the polishing padat a rate of 250 ml/min. Upon completion of the polishing, thesemiconductor substrate was detached from the carrier, mounted in a spindryer, washed with distilled water, and then dried with nitrogen for 15seconds. The changes in the film thickness of the dried semiconductorsubstrate before and after the polishing were measured using a spectralreflectometer type thickness measuring instrument (SI-F80R, Kyence). Thepolishing rate was calculated using the following Equation. The resultsare shown in FIGS. 2 a and 2 b.Removal rate (Å/50 seconds)=difference in thickness before and afterpolishing (Å)/polishing time (50 seconds)

As shown in FIGS. 2 a and 2 b , the polishing pads of the Examples wereexcellent in the initial polishing rate at an appropriate level, whereasthe polishing pads of the Comparative Example had excessively highinitial polishing rate due to the increase in the aggregation of hardsegments. Thus, the polishing pads of the Comparative Examples areexpected to sharply decrease in the polishing rate due to the padglazing phenomenon.

(9) Pad Cut Rate

Each polishing pad was pre-conditioned with deionized water for 10minutes and then conditioned with deionized water for 1 hour. The changein thickness of the polishing pad during the conditioning was measuredto calculate the pad cut rate. The equipment used for conditioning wasCTS AP-300HM. The conditioning pressure was 6 lbf, the rotational speedwas 100 to 110 rpm, and the disk used for conditioning was SasolLPX-DS2. The results are shown in FIGS. 3 a and 3 b.

As shown in FIGS. 3 a and 3 b , the polishing pads of the Examples hadan excellent pad cut rate at the time of conditioning with a diamonddisk, whereas the polishing pads of the Comparative Examples had a lowpad cut rate due to the increase in the aggregation of hard segments.

The invention claimed is:
 1. A composition, which comprises aurethane-based prepolymer, a curing agent, and a foaming agent, whereinthe urethane-based prepolymer comprises a prepolymerization reactionproduct of at least one diisocyanate monomer and at least one polyol,the at least one diisocyanate monomer comprises at least one aromaticdiisocyanate monomer, and the urethane-based prepolymer comprises anunreacted diisocyanate monomer in an amount of 5% by weight to 13% byweight based on the weight of the urethane-based prepolymer.
 2. Thecomposition of claim 1, wherein the urethane-based prepolymer comprisesthe unreacted diisocyanate monomer in an amount of 9% by weight to 11%by weight based on the weight of the urethane-based prepolymer.
 3. Thecomposition of claim 2, wherein the urethane-based prepolymer comprisesan unreacted aromatic diisocyanate monomer in an amount of 2% by weightto 4% by weight based on the weight of the urethane-based prepolymer. 4.The composition of claim 1, wherein the urethane-based prepolymercomprises an unreacted NCO group in an amount of 5% by weight to 13% byweight and an unreacted aromatic diisocyanate monomer in an amount of0.1% by weight to 5% by weight, based on the weight of theurethane-based prepolymer.
 5. The composition of claim 4, wherein theurethane-based prepolymer comprises the unreacted NCO group in an amountof 7% by weight to 10% by weight based on the weight of theurethane-based prepolymer.
 6. The composition of claim 5, wherein theurethane-based prepolymer comprises the unreacted aromatic diisocyanatemonomer in an amount of 1% by weight to 3% by weight based on the weightof the urethane-based prepolymer.
 7. The composition of claim 1, whereinthe urethane-based prepolymer comprises an aromatic diisocyanate monomerin which two NCO groups are reacted in an amount of 10% by weight to 40%by weight based on the total weight of the at least one aromaticdiisocyanate monomer.
 8. The composition of claim 7, wherein theurethane-based prepolymer comprises the aromatic diisocyanate monomer inwhich two NCO groups are reacted in an amount of 15% by weight to 25% byweight based on the total weight of the at least one aromaticdiisocyanate monomer.
 9. The composition of claim 7, wherein theurethane-based prepolymer comprises an aromatic diisocyanate monomer inwhich one NCO group is reacted in an amount of 50% by weight to 80% byweight based on the total weight of the at least one aromaticdiisocyanate monomer.
 10. The composition of claim 9, wherein theurethane-based prepolymer comprises the aromatic diisocyanate monomer inwhich two NCO groups are reacted and the aromatic diisocyanate monomerin which one NCO group is reacted at a weight ratio of 0.2:1 to 0.5:1.11. The composition of claim 1, wherein the at least one aromaticdiisocyanate monomer comprises toluene 2,4-diisocyanate and toluene2,6-diisocyanate, and the urethane-based prepolymer comprises unreactedtoluene 2,6-diisocyanate in an amount of 0.1% by weight to 3% by weightbased on the weight of the urethane-based prepolymer.
 12. Thecomposition of claim 11, wherein the urethane-based prepolymer comprisestoluene 2,4-diisocyanate in which two NCO groups are reacted in anamount of 10% by weight to 30% by weight based on the total weight ofthe at least one aromatic diisocyanate monomer.
 13. The composition ofclaim 11, wherein the urethane-based prepolymer comprises toluene2,4-diisocyanate in which one NCO group is reacted in an amount of 50%by weight to 65% by weight based on the total weight of the at least onearomatic diisocyanate monomer.
 14. The composition of claim 11, whereinthe urethane-based prepolymer comprises toluene 2,6-diisocyanate inwhich one NCO group is reacted in an amount of 10% by weight to 20% byweight based on the total weight of the at least one aromaticdiisocyanate monomer.
 15. The composition of claim 1, wherein the atleast one diisocyanate monomer comprises at least one aliphaticdiisocyanate monomer, and the urethane-based prepolymer comprises theunreacted aromatic diisocyanate monomer and the unreacted aliphaticdiisocyanate monomer at a weight ratio of 0.05:1 to 0.7:1.
 16. Thecomposition of claim 1, which has a gelation time of 80 seconds to 130seconds and has, upon curing, a tensile strength of 10 N/mm² to 23N/mm², an elongation of 80% to 250%, and a hardness of 40 Shore D to 65Shore D.
 17. A process for preparing a polishing pad, which comprisespreparing a first raw material composition comprising a urethane-basedprepolymer, a second raw material composition comprising a curing agent,and a third raw material composition comprising a foaming agent;preparing a raw material mixture by sequentially or simultaneouslymixing the first raw material composition with the second raw materialcomposition and the third raw material composition; and injecting theraw material mixture into a mold and curing it, wherein theurethane-based prepolymer comprises a prepolymerization reaction productof at least one diisocyanate monomer and at least one polyol, the atleast one diisocyanate monomer comprises at least one aromaticdiisocyanate monomer, and the urethane-based prepolymer comprises anunreacted diisocyanate monomer in an amount of 5% by weight to 13% byweight based on the weight of the urethane-based prepolymer.
 18. Apolishing pad, which comprises a polyurethane resin and a plurality ofmicropores dispersed in the polyurethane resin, wherein the polyurethaneresin is derived from a urethane-based prepolymer, the urethane-basedprepolymer comprises a prepolymerization reaction product of at leastone diisocyanate monomer and at least one polyol, the at least onediisocyanate monomer comprises at least one aromatic diisocyanatemonomer, and the urethane-based prepolymer comprises an unreacteddiisocyanate monomer in an amount of 5% by weight to 13% by weight basedon the weight of the urethane-based prepolymer.
 19. The polishing pad ofclaim 18, wherein the micropores have an average size of 20 μm to 25 μm,and the polishing pad has a polishing rate of 3,500 Å/50 seconds to5,000 Å/50 seconds.
 20. A process for preparing a semiconductor device,which comprises polishing the surface of a semiconductor substrate usingthe polishing pad of claim 18.